1. Field of the Invention
This invention relates to a method for measuring a thickness of an oxide film formed on a substrate, which is suitably applied for evaluating a thickness of a transistor gate oxide film.
2. Description of the Related Art
Recently, a thickness of a MOS transistor gate oxide film in an LSI has been thinned to be less than 100 Å to comply with requirements for an improved integration density and an increased speed. Therefore, it has been required and examined to measure the thinned gate oxide film accurately in view of reducing a measurement error. Widely known methods for measuring a thickness of a gate oxide film are an ellipsometry utilizing a polarization analysis, a nano-spectroscopy utilizing an optical interference method, and the like (“University Course of Electricity Institute, Electronic Material Engineering”, P. 228-231, written by Institute of Electricity Communicational Education, and “Applied Physics Selection, 3. Thin Film”, P. 200 to 203, written by S. Kanbara and H. Fujiwara). In the ellipsometry, light is irradiated on the gate oxide film by an optical instrument to detect a refractive index and an absorption coefficient, and the thickness of the gate oxide film is measured based on the refractive index and the absorption coefficient.